With a sharp increase of communication traffic, the authorized spectrum of 3GPP (3rd Generation Partnership Project) is increasingly insufficient to provide higher network capacity. To further improve the utilization rate of spectrum resources, 3GPP discusses that how to use unauthorized spectrum with the help of authorized spectrum such as 2.4 GHz and 5 GHz frequency bands. These unauthorized spectrums are currently mainly used by systems of Wi-Fi, blue-tooth, radar, medical and the like.
Generally, access technologies like LTE (Long Term Evolution) designed for an authorized frequency band are unsuitable for use at unauthorized frequency bands, because access technologies such as LTE has high requirements on spectrum efficiency and user experience optimization. Nevertheless, CA (Carrier Aggregation) function makes it possible to deploy LTE at unauthorized frequency bands. 3GPP has put forward the concept of LAA (LTE Assisted Access), which can use unauthorized spectrum with the help of LTE authorized spectrum. While the unauthorized spectrum has two operating manners, one is SDL (Supplemental Downlink), namely there is only downlink transmitting sub-frame; the other is TDD (Time Division Duplexing), which includes both downlink sub-frames and uplink sub-frames. SDL can only be used with the help of CA technique. However, TDD can be used with the help of CA, DC (Dual Connectivity) or be used independently.
Compared with Wi-Fi system, a LTE system working at the unauthorized frequency band can provide higher spectrum efficiency and greater coverage effect. Besides, data traffic can be seamlessly switched between the authorized frequency band and the unauthorized frequency band based on the same core network. This means better broadband experience, higher speed, better stability and mobile convenience for users.